# Full text of "QUEST - PART 2 - LEARNING SCIENCE BY DOING"

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Materials

will observe that the palms have warmed
up.

Students to enquire

1. Why do the palms get warm when
rubbed together ?

2. What is the primary source of
heat energy ?

What to do ?

1. Rub your palms a number of times. You

1. When the palms are rubbed there
is friction between the palms, and
the molecules in the palms start
vibrating faster. Owing to this
heat is generated and the tem-
perature increases.

2. Muscle energy makes the palm
move. Muscle energy is obtained
through the intake of food. Plants
prepare food through photosyn-
thesis. Hence, solar energy is the primary
source of heat energy.

Quest 48

Materials

1. Two corks

2. 10cm. aluminium wire-1

3. 4cm. aluminium wire-2

4. Candle and matches

What to do ?

1. Insert the aluminium wires into the codes as

shown in the figure.

% *

2. Hold the two ends of the aluminium wires
with the two hands. Bring the other two
ends together.

2. Why can you hold die wire B for a long
time ?

3. How was heat conducted along the wire A ?

4. If you had held the wire A wrapped with
paper or cloth, how would you have felt the
heat ?

Explanation

1. Aluminium is a good conductor of heat
Hence, it is heated quickly. Hence, you can
not hold the wire A for long.

2. Wire B has two parts connected through a
cork. Cork is a very bad conductor of heat.

%

the junction of the two wires so that both
the wires are equally heated.

4. You will observe that it will be difficult for
you to hold the single wire A for a long time.
The wire A is heated much faster than the
wire B with two smaller wires.
Students to enquire
1 . Why can not you hold the wire A for a long
time ?

Hence, the heat of the part heated by the
candle can not reach quickly to the other
part of the wire B held with the hand .

3. The process of heat flow along the wire A
is called conduction.

4. Paper and cloth are bad conductors. Hence,
if you hold a wire wrapped with paper or
cloth, it will take much longer time for the

-

Quest 49

Which heats up first-2

ii

to

Materials

1. 15-20cm. long thin (2-3mm dia) wires of
copper, aluminium and iron having the same
length and diameter.

2. Candle and matches.

What to do ?

1 . Tie one end of each wire together.

wires by the lighted candle.

2. Which of the parameters you have to keep
constant ?

3. For which difference in the property of the
materials could you perform the
experiment ?

Explanation

1 . Copper conducts heat the most and iron, the
least.

2 . In this experiment the length and diameters

3. After half a minute or so touch the ends of
the wires and try to observe which one is
heated most You will observe that the copper
wire will be heated the most and the iron
wire, the least.

Students to enquire

mmm

1 . Which metal conducts heat the fastest ?

of the wires and the heat applied to the three
wires were kept constant.

3. The conductivity of different materials is
different. The conductivity of a substance
depends upon its molecular structure. The
difference in the property of substances was
utilised to conduct the experiment.

Quest 50

The cloth that does not

burn

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Materials

1 . A 50 paise or 1 rupee coin

2. A piece of old doth

3. Candle and matches .
What to do ?

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to **k/to\Si^to J

the coin for a long time, will the cloth bum ?

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1 . Keep the cloth stretched and hold the candle
on the cloth. Observe how easily it bums .

2. Now, wrap the

cloth tightly over -~prs.

the coin and hold j. \

hand. Hold the —
lighted candle on j/S

the cloth for a tr (cs '

few seconds. ,S \\J

The cloth is not

burnt. / | /

3. Remove the

cloth and touch |

the coin. You l j l

will feel it hot. |i I

Students to 1

t-l
Citi

in

i

i

enquire i®

1 . Why is it easier ^

to bum the cloth

without the coin ? .

2. Why does not the cloth bum when the coin
is there ?

3. Why does the coin heat up ?

4. If instead of a coin a piece of wood or
plastic was taken, what would have hap-
pened to the cloth ?

5. If the candle is held on the cloth wrapped on

mill

Explanation

1. The flame of the candle could raise the

to

*

temperature of the cloth above its ignition
point. Hence, the cloth burnt.

2 . A metal is a good conductor of heat. Hence,
when the lighted candle was held on die

cloth wrapped

&

on a coin, the
heat from the
flame would
gs conduct quickly

/ to the coin.

/ Owing to this the

temperature of

the cloth could
not rise above

the

ignition

r\ . .M point. Hence the

\V<r cloth did not

^ bum.

" < 3. As a metal is a

good conductor
of heat, the coin

got heated.

4. Wood and plastic are bad conductors of
heat. Hence, the temperature of cloth will
rise above ignition point and the cloth will
bum.

5. If the candle is held on the cloth wrapped
on the wire for a long time, the temperature
of the cloth will rise above the ignition point
and the cloth will bum.

Quest 51

Materials

1 . A 4"x4 M piece of cloth

2. A metal plate
What to do ?

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► # * • •.

1. Place one of your hands on the cloth and the

Explanation
1. A metal is a better conductor of heat
than cloth. Normally, body temperature
is more than the outside temperature.

When you touch both the objects with

other on the plate. You will observe that
though both the materials are at the same

room temperature, the metal plate feels

*

cooler.

two hands the metal takes away heat from
your body quicker than the cloth. Because
of this your hand feels the metal cooler
than the cloth.

m

Students to enquire

1. Whydoyoufeeltheplatecoolerthanthecloth?

Quest 52

Materials

1 . Four empty cold drink bottles

2. Colouring material
What to do ?

1 . Fill the bottles A and B with cold water and
the bottles C & D with hot water.

2. Mix colouring material with the water of A
and D.

3. Close the mouths of the bottles B and C with

your thumbs. Bring the bottles over the
mouths of the bottles D and A respectively
and take off your thumbs from the mouths
of the bottles.

4. After some time you will observe that the
water in bottle B is getting coloured. But
there is no change in the colour of the water
in bottle C.

Students to enquire

1 . Why did the water in bottle B get coloured but
why did not the water in the bottle C do so ?

2. When will the water in bottle C get
coloured ?

3. If the water in all the bottles had been in the
same temperature, then what changes would
have happened to their colours ?

4. Why did all the bottles come to the same
temperature after some time ?

Explanation

1 . Density of hot water is less than cold water.

So the cold water of bottle B comes
down to bottle D and the hot water
of bottle D moves up to bottle B by
the process of convection. Thus the
colourless water in bottle B gets
coloured and the colour of water in
bottle D becomes lighter. But the
water in bottle C is hot and that in
bottle A is cold. Hence the cold water
in bottle A, being more dense, re-
mains in the bottom and the warm
water of bottle C tries to remain at
the top. So the water in the bottles
did not mix.

2. When the temperatures of bottles A
and C become equal owing to radiation,
exchange of water takes place between the
bottles through the process of diffusion and
the water in bottle C gets coloured.

3. When temperatures of all the bottles be-
come the same, water of all the bottles be-
come coloured through the process of dif-
fusion.

4. All the bottles will come to the same tem-
perature by the process of radiation.

- -***.

Quest 53

Materials

1 . Crushed ice

2. A large test

■

3. Asmallstor

2. The water along with the ice at the bottom
of the test tube is cold. Hence, its density
is more than the cold water. Hence, when

lamp

upper portion
heated water

rjf. r.

What to do ?

1. Fill one-third of the test tube with crushed
ice. Keep the stone over the ice in the test
tube to hold the ice.

2. Take a little water in

the test tube.

• •

3. Hold the test tube

t *

with the holder and
heat the upper por-
tion of the test tube
until the water starts

bottom. The

convection process docs not work. So the
ice always remains in contact with the cold

boiling.

4. You will observe that

water boils at 100° C
but the ice does not
melt

Students to enquire

1 . What is the purpose of keeping the stone ?

2. Why does not the ice melt when the water

boils ?

3. If the stone were not there, could the ex-
periment be conducted ?

4. Was the water conducting the heat well ?

5. Did the convection process work in

water ?

Explanation

1 . Ice could not float up because of the stone

over it.

water. Hence, the ice does not melt.

3. The experiment could not be performed if
the stone were not there. Without the stone
the ice would float up and it would melt
owing to the convection process.

4. Water is a bad conductor of heat. Hence,

when the upper portion of the test tube was

♦

heated, the water did not conduct the heat
to the ice well.

4. The convection process was not working as

always try

bottom

Quest 54

Materials

1. Two glass tumblers

thermometers

3. A piece of white paper and a piece of used

carbon

spot light

What

1. Cover one glass with the piece of white
paper and the other glass with the piece of

records the higher temperature.

Students to enquire

1 . Why does the glass covered with the carbon
paper get heated more ?

2. Normally, which colours of light are more
hot and cold ?

Explanation

1 . A black body absorbs more radiant energy
than a white body. A white body reflects all
colours of light but a black body absorbs

Take the same amount of water in the two

glasses and introduce the two thermometers
into the glasses.

3. Turn the spotlight on and keep the glasses
equidistant from the light so that both may

receive the same amount of light from the
lamp.

4. After 5-6 minutes record the temperatures
measured by the two thermometers. You
will observe that the thermometer in the
glass that is covered with carbon paper

all colours. The glass covered with the piece
of black carbon paper absorbs more radiant
energy from the lamp but the other glass
covered with the piece of white paper re-
flects away all colours. Hence, the water in
the glass covered with the carbon paper
gets heated more.

2. The warmer colours in descending order
are : red, orange, brown and yellow. The
sequence of cooler colours is : green, blue,
purple and violet.

Quest 55

Materials

1 . Two similar thermometers

2. A piece of cloth

3. A glass and some water

What to do ?

1. Record the temperatures measured by the
two thermometers.

%

2. Cover the bulb of one of the thermometers
with a piece of wet cloth. Take water in the
glass and dip this thermom-
eter in water.

Note the temperature as mea-
sured by the thermometer.

3. Note the relative humidity
from the weather reports in

the newspaper.

Students to enquire MM

1 . Is there any difference between
the temperatures recorded by
the dry bulb thermometer and
that with the wet bulb ? If so,

why

?

2. If the relative humidity is high,
what difference between the
temperatures measured by the
two thermometers will be

noticed ?

3. If the difference between the two tempera-
tures is much, what inference can you draw
about the relative humidity in the air ?

For evaporation the water draws heat from
its environment including the bulb of the
thermometer. For this the thermometer gets
cooled and there is a difference between the
dry and wet bulb thermometers.The drier
the air, the quicker is the evaporation and
the lower the temperature reading in the wet
bulb thermometer.

2. If the relative humidity in the air is high,

When the bulb of a thermometer is wet,
evaporation takes place from the wet cloth.

then there is practically no difference in
temperature between the dry & wet bulb
thermometers.

3. If the difference between the dry and wet
bulb temperatures is high, then it proves
that the relative humidity is low.

Quest 56

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Heat and temperature

Materials

1. Two elas

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5SSSSSSSS

tumblers

2. A heavy piece of iron

3. A big nail

4.

thermometers

5. Two toys

6. Two heaters

7. A beaker.

water in the glasses.

3. When the water in the beaker starts boiling
replace the piece of iron and the nail from
the beaker to the two glasses with the aid

Keep the thermometers

the water.
Record the

till the rise in temperature stops.

What to do ?

1 . Put the piece of iron and the nail in the water
in a beaker and boil the water.

2. Take the same amount of water (100 c.c.)
in the two glasses. Measure temperatures
by placing the two thermometers into the

Students to enquire

1 . What were the temperatures of water in the
two glasses before the introduction of the
piece of hot iron and the nail ?

2. When the water starts boiling what is its
temperature ?

Quest 57

3. After the hot iron objects are transferred to
the glasses, water in which glass becomes
hotter ?

4. Why did the temperatures of water in the
glasses rise ?

5 . Out of the two iron pieces which one has

more thermal capacity ?

water in the glasses the one with the bigger
object rises to a greater temperature com-
pared to the other one.

4. The

the conduction of heat from the hot object

to the water.

5. The bigger iron object has greater thermal

What are the factors on which thermal
capacity depends ?

1. Before the hot metal objects were placed,
the temperatures of water in both the glasses
were the same, i.e., the normal room tem-
perature .

2. The temperature of boiling water is 100°C.

3. When the hot objects are transferred to the

capacity than the smaller one because of its
greater mass. So heat in the bigger object
is more than the smaller one. Hence, the
water in the glass in which the bigger object
is placed rises to a greater temperature.

6. The thermal capacity of an object depends
upon its mass and the material of which the

Quest 58

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jm

Materials

1. A 100 ml conical flask with a rubber stop-
per and a tube passing through it

2. A heater or a spirit-lamp

3. Ink and crushed ice

What to do ?

1 . Fill the flask with coloured water. Gose the
mouth of the flask tightly with the stopper.

2. Heat the water in the flask. You will observe
that the coloured water is rising in the tube.
Be careful that air cannot enter the flask.

3 . Now, keep the flask in crushed ice. You will
observe that the coloured water in the tube
is going down.

Students to enquire

1 . Why do you have to stop entry of air inside

2. Why is there a change in the height of water
in the tube due to heating or cooling ?

3. Can you compare it with a real
thermometer ?

4. How can you calibrate this improvised ther-
mometer ?

Explanation

1 . The flask has to be air tight so that when
the water expands as a result of heating it
cannot escape from anywhere except through
the tube.

2. Most of the materials -solids, liquids or gases
expand on heating and contract on cooling.
As water cannot escape, it rises in the tube on
heating and comes down on cooling.

3. It is an analogue of a thermometer.

4. To calibrate the thermometer keep the flask
on crushed ice. You will observe that the
water will start coming down and will stop
at a certain height. Tie a rubber band to
show the height. That will mark 0°C. Take
out the flask from ice and after some time
heat the flask for the water to boil. Water

will rise in the tube and stop at a particular
height. Tie a rubber band to show that height.
That marics 100°C.Now you may divide 0°
to 100° at equal intervals. You have made

Quest 59

Materials

1. An alcohol thermometer

2. Ice cubes

3. A heater

4. A beaker

What to do ?

msm
mm

1. Take a few ice cubes in a beaker and
introduce the thermometer into the ice cubes
(fig.A). Observe what happens to the alco-
hol in the thermometer. Keep measuring the
temperature at intervals of one minute till
all the ice melts into water. Measure the

4. Measure the temperature of the steam that
comes out of the boiling water.

: msm

Students to enquire

1 . When the thermometer is kept in the ice for
some time, what is the temperature of ice?

2. What is the temperature of ice till it melts
completely ?

3. What is the temperature of boiling water ?

4. What is the temperature of the melted water
after it has been kept for some time ?

5. What is the temperature of the steam com-
ing out of the boiling water ?

temperature of the melted water after 10 or
15 minutes.

2. Now place the beaker with water on the
heater (fig. B), insert the thermometer in
water and heat it. Do not insert the ther-
mometer in boiling water.

3. Observe what happens to the alcohol in the
thermometer. Observe the temperature when
the water starts boiling. Keep the water
boiling for half a minute and observe what
happens to the temperature.

Explanation

1 . When the thermometer is kept in the ice for
some time it will show 0°C temperature.

2. As long as all the ice is not melted, the
thermometer will show 0°C temperature.

3. The temperature of boiling water is 100°C.

4. When the melted water is kept for some

5. The temperature of steam coming out of
boiling water is 100°C.

Quest 60

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Melting point

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Materials

1 . A big block of ice

2. A one meter long wire

3. Two bricks or heavy objects

What to do ? IIHS««^«
' 1 . Keep the block of ice on some object in
such a way that its edges project outside.

2. Tie two heavy weights at the two ends of
the wire and hang it in such a way that the
wire passes through the centre of the ice
block.

the pressure of wire on the ice ?

If the ice block is small, will the wire cut
through the ice quicker ?

If the weights connected to the wire is in-
creased, will the wire cut through the ice
quicker ? If so, why ?

3 . After some time you will observe that the
wire has cut through the ice. But as the wire
cuts through, the ice above the wire joins
together.

4. When the wire cuts completely through the
ice, it again joins together into one block.

Students to enquire 18 B— 1^^^

1. Why docs the wire cut through the ice ?

2. What happened to the melted water above
the ice ?

3 . Which property of the ice is changed due to

Explanation mmmmMmmmmmmM

1 . The melting point of a solid is lowered when
the pressure on it is increased. The wire
exerts pressure on the ice. Hence the melting
point of ice, where the wire exerts pressure

on the ice, is de-
creased. For this the
ice below the wire
— ] melts and the wire

/ cuts through the ice.

2. After the ice melts
/ because of the low-

ering of the melting
point and the wire
cuts through the
s* melted water which

is at 0°C the water

freezes up again.

3. If pressure is increased on a solid, its melt-
ing point decreases.

4. If the block is small and the weight on the
wire remains the same, then the wire will cut
through quickly. For, in such a case pres-
sure at a particular point will increase.

5. If the weight connected to the wire is in-
creased, then the wire will cut through the
ice quickly because pressure at a particular
point will increase.

Quest 61

Materials

1. A small (100 c.c.) beaker

2. A thermometer and a spoon

3. A heater or a spirit-lamp

What to do ?

1 . Heat about 2cc of water in a beaker. Mea-
sure the temperature of the water every half
a minute and keep a note of it.

2. When the water starts boiling, mix about 2
gms. of salt with the water.

3 . Continue heating the water and
stir the water with the spoon.

Note the temperature of water
every half a minute till the
water starts boiling.

4. Repeat the same experiment
with 4 gms. and 6 gms. of salt.

Students to enquire

1. What is the boiling point of
water at normal atmospheric
pressure ?

2. After salt is mixed, what hap-
pens to the temperature of the
solution ?

3. What is the boiling point of
the solution ?

4. Why does the boiling point increase ?

5. What happens when you repeat the experi-
ment with 4 gms. or 6 gms. of salt ?

Explanation

1. At ordinary pressure the boiling point of
water is 100°C.

2. When salt is mixed with the water while it

is boiling, the boiling stops and the tem-
perature of water falls. Salt takes some heat
from the water to melt. Because of this the
temperature falls and the boiling stops.

3. The boiling point of the solution is increased.

4. Salt gets ionised in water. Water molecules
keep together owing to cohesion. Water
molecules attach also to sodium chloride
ions. Owing to this it becomes difficult to

conduct heat and the boiling stops. This
causes the increase of the boiling point.

5 . The more the salt, the more is the increase
of the boiling point of the solution. But if
the temperature of the steam coming out is
measured, it will be 100°C.

Quest 62

Materials

1. A glass tumbler and a spoon

2. A thermometer

3. Ice cubes and water
What to do ?

1. Take a glass of water and drop a few ice

cubes in it Keep a thermometer in the water
and note the temperature at regular inter-
vals.

humidity in the air is low ?

4. Where do we find a similar event in our
daily life ?

Explanation

1 . Dew comes from the air. Ice cools the glass.
So, the water vapour in the atmosphere gets
condensed into water droplets when it comes
in contact with the cool glass.

2. If the dew point is measured in different

2. Observe the outside of the glass carefully.

3. Stir the water with the spoon and observe
at what temperature the dew appears out-
side the glass.

Students to enquire

1. From where does the dew come on the
outside of the glass ?

2. At what temperature is the dew formed ?

3. Will the dew point be higher or lower if the

seasons at different periods of the day or the
year, it will be observed that the dew point
will be different.

3 . The drier the air, the lower is the dew point.

4 . In winter we observe that dew forms on the
grass early in the morning. In the night the
earth cools and when the water vapour in
the air comes in contact with the cool earth,
it condenses into water droplets.

Quest 63

mmmm

Materials

1. A cup

2. A thermometer (-10°C to 50°C)

3. Salt

4. Ice

What to do ?

1. Fill the cup with ice
cubes and insert a ther-
mometer in the ice.

Crushed ice will be bet-
ter.

2. You will observe that
after some time the ther-
mometer will show 0°C
temperature. The ther-
mometer will not go
down further, no matter
how long you keep the
thermometer in the ice.

3. Now, mix salt with the
ice and stir the mixture. Notice the ther-
mometer reading. You will observe that the
terriperature will go down to about -10°C.
Some of the ice will melt quickly.

Students to enquire

Explanation

1. Normally, ice melts at 0°C.

2. The melting or freezing point of ice and salt
solution is always lower than pure water.
So, when salt is mixed, the ice melts at 0°C

mmm

1. Normally, at what temperature does ice
melt ?

2. Why does ice melt when you mix salt with
it ?

3. When ice melts on addition of salt, is heat

4. Is heat added or extracted while the ex-
periment is conducted ?

as the freezing point gets lowered.

3 . Ice needs heat to melt. But as no heat has
been aided to the ice from outside, it ex-
tracts heat from its environment to melt. A
similar event occurs when water is kept in
an earthen pitcher. Water oozes through the

evaporates

pot

earthen pitcher

is cool during summer.

4 . In this experiment no heat has been supplied
from outside. Heat has been extracted from
the ice itself.

Quest 64

Materials

1 . Ether or alcohol

2. A* straw

3. A thin steel glass

4. A thin wooden board

1 . Wet the wooden board with water.

2. Take a little ether or alcohol in the glass and

keeD it on the wooden board.

w.

Students to enquire

1. Why does the glass get cooled when you
blow air through the alcohol or ether ?

2. Why does the glass get stuck to the board ?

3. Why does the experiment work better with
coconut oil ?

1 . When the air is blown through the alcohol
or ether, it gets evaporated quickly. For

3. Now insert a straw in the liquid and keep
blowing air through it. You will observe
that bubbles will come up through the ether.

4. After blowing for a while, you will observe
that the glass has become very cool and it
has stuck to the board. If you raise the glass
the board also will come up with it.

5. If you wet the board with coconut oil.then
the experiment will work better.

evaporation latent heat is required. The latent
heat is taken away from the ether or alcohol
and glass. Because of this the liquid and the
glass get cooled.

2 . When the glass becomes too cold, the water
in the board below the glass gets cooled and
forms ice. For this the glass gets stuck to
the board.

Be careful : Ether or alcohol is highly inflammable.

Quest 65

Materials

1. A table fan

2. Two alcohol thermometers
What to do ?

1 . Note the temperatures recorded by the ther-

mometers.

2. Keep the thermometer A in the wind in front
of the fan. Keep the thermometer B at the
back of the fan.

3. Keep the fan blowing for some time and
then mark the temperatures recorded by both
the thermometers. You will observe that
both the thermometers show the same read-

ing.

4. Now wrap the bulb of the thermometer A
with a wet cloth and switch on the fan. If
the temperature is measured after a few
minutes you will observe that the tempera-
ture recorded by the thermometer A is less
than that recorded by thermometer B.

Students to enquire

1 . When the fan is turned on before the bulb
of the thermometer A has been covered with
the wet cloth, why is there no difference
between the temperatures recorded by the
two thermometers ?

2. When the bulb of the thermometer A is
wrapped with the wet cloth, why does it
record a lower temperature ?

3. Why do we feel cool when the air blows ?

sills

Explanation |

1 . Apparently, it might seem that when air

blows, the thermometer A should reach a
lower temperature. But if the temperature is

thermometer

the thermometer A will

temperature. The temperature in thermom-
eter A will rise because of friction between
the thermometer bulb and the blowing air.

2. But when the bulb is wrapped with the wet

cloth, water evaporates from the cloth. For
evaporationheatis taken away from thebulb.
When air blows from the fan, the saturated
ai r round the bulb is driven away . Hence a
lower temperature is shown by the thermom-
eter A.

3. When the air blows, sweat evaporates more
quickly. Hence we feel cool. During the
summer when the air is humid, the air round

our body remains saturated with water
vapour. Then the evaporation of sweat from
the body stops. Hence we feel uncomfort-
able. But. if the air blows, the saturated
air is driven away. More evaporation of
sweat takes place and we feel comfortable.

Quest 66

mr

Materials

1. An ice cube

2. Salt

What to do ?

1 . Keep the ice on the table and place a thread
along the centre line of the ice cube.

2. Sprinkle some salt on the thread.

3. After a little while try to raise the thread
carefully. You will observe that the ice cube

will come up along with the thread.

4. You will observe that the ice has melted at
the place where the salt is sprinkled. But the
melted water will solidify into ice again
after a while.

Students to enquire

1 . At what temperature does the ice melt ?

2. How could you lift the ice cube ?

3. Where in our daily life do we use the prop-
erty of lowering the melting point of ice with
the help of salt ?

4. In cold countries when the road is covered
with snow, salt is sprinkled on the road, why?

Explanation

1 . Ice melts at 0°C.

2 . The melting or freezing point of saline water
is less than pure water. Hence, when salt is
sprinkled, the ice around the thread melts.The
temperature of melted water is less than 0°C

9

When a considerable quantity of ice melts,
the concentration of salinity of water re-
duces. For this the freezing point of the
solution comes near to 0°C. But as the tem-
perature of the water is then a few degrees
below 0°C it freezes again and the thread
gets stuck to the ice.

3. When ice cream is made at home, a tem-
perature lower than 0°C is achieved by
mixing salt with the crushed ice. Owing to
this the liquid mixture that makes the ice

4.

cream

formed

roads during winter time it becomes diffi-
cult to drive a car. The car skids while
moving. When the car moves on ice it
exerts pressure on the ice. We know that the
freezing point of water goes down with
increased pressure. Because of this, the ice
below the tyres melts, the road becomes
slippery and the car skids. To avoid skid-
ding salt is sprinkled on the ice. Salt lowers
the temperature of ice below 20°C. Hence,
when a car moves on the ice, though the
freezing point of water goes below 0°C the
ice does not melt as its temperature is al-
ready much below 0°C because of the sprin-
kling of salt.

Quest 67

Materials

1. Matches

2. Ice cubes

3. A small beaker(100cc)

4. A spirit lamp or a heater

5. A candle

What to do ?

1 . Light the candle. You will observe that wax
will start melting. After some time you will
observe that gas is com-
ing out of the molten
wax.

2. Blow off the candle.

You will observe that
the gas is coming out.

Bring a lighted
matchstick near the
gas. You will observe
that the candle will
catch the flame.

3. Take a small piece of
ice in a beaker and heat
it. You will observe that
the ice will melt into
water and after some
time water will convert
into steam.

Students to enquire

1 . What do you understand by the melting and
gasification of wax by heat ?

2 . Why does the candle burst into flame when
you bring a lighted matchstick near it when
it has just been put out ?

What

formation of steam

to heat ?

Explanation

formation

gas one can understand that heat changes
the state of matter.

2. After a candle is put out, wax gas comes
out for some time .When a lighted matchstick

ignited

flame

3. The cl
steam

matter. It also shows that matter has three
states - solid, liquid and gaseous.

Quest 68

Materials
1. A 3 m. long iron wire
2 A 500 gm. weight

3. A scale

4. Matches

5. Six candles

6. Two chairs

7. A paper arrow

8 . A clip or a little cellotape

*

2. Will there be any change in the amount of
lowering of the arrow if the numbers of
candles are changed ?

3. Will the amount of lowering depend upon
the material of the wire ?

4. Give some examples of expansion by heat

Explanation

1 . When you heat the wire, it expands in length.

Jill

What to do ?

1 . Tie the wire to the chairs and keep it taut.

2. Hang the weight with a string from the
middle of the wire. Attach the paper arrow
to the string or the weight with the clip or
the cellotape respectively so that it may
show height on the scale.

different places with the lighted candles.
You will observe that the arrow will gradu-
ally go down.

Students to enquire

1. Why will the arrow go down ?

Hence the arrow will go down.

2. The wire will extend more if the number

/

of candles are increased. The arrow will go
down.

3. Different materials expand differently with
the same amount of heat. Copper will expand
more.

4. To prevent the railway lines from buck-

• ^

ling, a small gap is left between two suc-
cessive rails to allow for expansion of the
lines when heated. The same precaution is
taken when placing steel bands round cart-
wheels.

Quest 69

Materials

1. A 50 c.c. pipette

2. A glass tumbler

3. A heater
What to do ?

!»■

mm & *

1. Heat some water and take the hot water in

the glass.

Students to enquire

1. Why does the watercome out like a spray ?

2 . Why is it that the water does not come out like
a spray when you invert the pipette slowly ?

Explanation
1 . When the pipette is suddenly inverted and

hot water starts descending, it heats up the

2. Draw by mouth the hot water in the pipette
(half of it).

3. Then close the open end with your thumb
and quickly draw out the pipette from the
hot water and invert it.

4. You will observe that hot water comes out
of the nozzle end like a spray.

5. Invert the pipette slowly and observe what

happens.

This

This

So

water comes out like a spray.
2. When you invert the pipette

air does not get trapped. Hence a higher
pressure is not created to force the water

out.

Quest 70

Materials

1 . An empty shoe-box

2. A candle, a match-box and some incense
sticks (agarbattis)

3. A transparent plastic sheet

4 . Two hard cardboard cylinders ( 1 5 cm. high)

5. Some cellotape

What to do ?

1 . Cut open one long side of the shoe-box and
cover it with the plastic sheet so that the
inside may be visible. Fix the two cylinders
on the top of the box as shown in the figure.

2. Place the candle first below the chimney A
and light the candle. If there is any opening
cover it with cellotape.

3 . Light two incense sticks and hold them over
the chimney B. Do not hold the sticks just
above the chimney. Blow the incense smoke
near the chimney B. Observe how the smoke
travels.

Students to enquire

1 . Why does the smoke come down the chim-
ney B ?

2. How can you make the air circulate between
the two chimneys without the lighted candle?

3 . Where on earth do we find an example of
this experiment ?

Explanation

1. The air around the
lighted candle gets
warm, becomes light
and rises up the chim-
ney A. Owing to this a
partial vacuum is cre-
ated inside the box.
This causes the incense
smoke to enter through
the chimney B into the
box to fill up the
vacuum. A draught is created inside from
chimney B to chimney A and the smoke
goes up the chimney A.

2. If we hold an ice cube over the chimney B,
then the air round it becomes heavy and will
go down the chimney B and a wind current
will be created.

3. In the daytime the land gets heated and the light
air goes up creating a partial vacuum. Cool
air from the sea rushes towards the land cre-
ating an air current. In the night the land be-
comes cool quicker than the sea. Then the cool
air from the land blows towards the sea.

Quest 71

Materials
1. A powerful torch
2 : A daik room

What

1 . Focus the torchlight straight on the wall and
notice the brightness of the spot of light.

2. Now throw the light on the same spot
obliquely. You will
observe that the light
wider area and the
brightness per unit area
has decreased.

Students to enquire

1. Why does the bright-
ness differ when the
light falls on the wall
obliquely ?

2. What relationship is
there between this
experiment and the
change of season ?

Explanation

1. The amount of light
energy coming out of
the torch remains the
same whether it falls straignt or ootiqueiy
on the wall. But when the light falls
slantingly it is distributed over a wider area.
Hence the amount of light per unit area is
less. Because of this the brightness is de-
creased when light falls slantingly.

2. When the earth resolves round the sun, the
same phenomenon occurs . The axis of earth
is at an angle of 66 %° with the ecliptic
plane. From 22nd March to 23rd September
the sunlight falls at right angles on different
latitudes on earth upto 237 2 °N. Hence the
northern hemisphere has summer during this

period. But from 23rd September to 22nd
March the sunlight falls at right angles on
different latitudes in the southern hemisphere.
During this period the southern hemisphere
has summer and in the northern hemisphere
where the sunlight falls obliquely is winter.

Quest 72

v/?^y^A<<-VA</^M\w y/Mv&uxt.

SSSi

/ ■ PL* ■ .P • » • f 7 'a S a v a • * » r. A*i r'^fcV’F* *

r • • * • • • * »-•-*•' • A A A AT M ■ • ■

AV.' * * •*••••». ^ J a wx w a r^H

1

■ •>»:*:.*: ;• : v >; . •;

< tu 5 tx< \$ >cj g rs

Magnetic and
Non-magnetic substances

v*v*v

Materials

1 . A bar magnet

2. Different materials; a nail; a pin, a piece of
rubber, a balloon, a piece of chalk, a piece
of copper wire, a piece of aluminium foil,
a matchstick, a marble, a 10 paise coin and

a piece of paper

not attracted by the magnet
Students to enquire

1 . What are the names of the objects that are
attracted by the magnet ?

2. What are the names of the objects that are
not attracted by the magnet ?

3. Prepare a table of objects based on their

What

w

1 . Spread the objects on the table. Touch each
object with the magnet one by one.

2. Keep the objects which are attracted by the

magnetic properties.
Explanation

magnet

are

1 . The objects which are attracted by the mag-
net are called magnetic substances.

2. The objects which are not attracted by the
magnet are called non-magnetic substances.

Quest 73

Materials

1 . A bar magnet

2. Iron filings

What to do ?

1 . Take some iron filings on a piece of paper

2. Bring the magnet over the filings but b e
careful not to touch them.

Observe where in the
magnet the filings are
attracted most.

3. The experiment works
well if the bar magnet is
long (4"-6") and is weak.

Students to enquire

1. Where do most of the

middle portion practically no ir
are attracted. If the bar magnet
nd lone, the effect can be seen mu

better.

3. The ends where the attraction is the maxi-
mum are called the poles of a magnet.

The central portion of the magnet where no

filings accumulate on the

magnet

2

portion

cally no iron filings are
attracted ?

3. What are the ends where
most of the iron filings
are collected called ?

4. What is the name of that
portion of a magnet where
no iron filings are at-
tracted ?

5. Which property of a magnet is understood
by this experiment ?

Explanation ■■■■MHI

1. Most of the filings are attracted at the ends

of a magnet.

neutral

zone.

5. The attractive property of a magnet is
undetstood by this experiment.

Quest 74

Materials

1 . A long bar magnet

2. A bent copper piece tied to a string
What to do ?

■MS:

fill

1 . Place the bar magnet on the bent copper
piece and allow it to hang horizontally by
holding the string.

will see that the magnet again turns and
shows the north-south direction.

Students to enquire S
1 . Why does the magnet come to show the
north-south direction every time ?

H*

Explanation
1 . Earth behaves as a big magnet with its poles

2. Observe that the magnet swings and then it
shows the north-south direction when it
comes to rest.

3. Swing the magnet slightly and observe that
it again shows the north-south direction.

4. Now, reverse the magnet and hang it. You

situated near the geographical north and
south. The magnetic field of the earth aligns
the hung magnet in the north-south direc-
tion. The end which points towards the north
is designated the north pole and the other
end, the south pole.

Quest 75

Materials

1 . A bar magnet

2. A magnetic needle
What to do ?

1. Keep the magnetic needle on the table. When
the needle comes to rest observe the direc-
tion the needle shows.

2. Why does the needle point to the same
direction ?

Explanation

V •’ SS.’S . \ ■-V.r.V/

1 . The needle always points towards the north-
south direction.

2. A needle is a very feeble magnet which can
move freely on a pivot. The earth behaves

2. Keep the bar magnet about 15 cm. above
the needle and rotate it so that the needle
starts rotating.

3. Stop the rotation of the needle and observe
the direction the needle shows.

Students to enquire

1 . To which direction does the needle point ?

like a huge bar magnet. The earth’s mag-
netic field aligns the magnetic needle in the
north-south direction. The end of the needle
which points towards the geographical North
is called the North pole and the other end
which points southwards is called the South
pole.

Quest 76

Magnetic attraction &

repulsion

Materials
1. Two magnets

What to do ?

1 . Normally, a bar magnet has in one end a
white spot which shows that the end is north.

4. Bring the north end of one magnet near the
south end of the other. Both magnets will
be attracted to each other.

Students to enquire
1 . Which is the surer test of magnetization —

Then the other end will be south.

Now bring the north end of one magnet near
the north end of the other magnet It will be
seen that the magnets are repelled.
Similarly repulsion occurs if south ends are
brought together.

attraction or repulsion ?

Explanation
1 . The surer test of magnetism is repulsion,
not attraction. A magnet will attract a mag-
netic substance at both ends. A magnetic
substance cannot be repelled by a magnet.

Quest 77

Materials

1 . A strong bar magnet

2. A long iron nail

3. Small nails

What to do ?

mm

1. Place small nails in a heap on a table.

2. Touch a bar magnet on the long iron nail
and then bring the pointed end of the nail
near the heap of
small nails.

3. The small nails will
cling to the long nail
in a chain.

4. Remove the magnet
from the long nail.

The small nails will
immediately fall.

Students to
enquire

1. Why does the long

nail attract

*

smaller nail when
the magnet touches
the long nail ?

2. Will a copper nail
or wooden nail at-
tract small nails ?

3. What is the process

zation called ?

The long nail will attract the small nails as
long as the bar magnet touches the long nail.

The nail becomes a temporary magnet.

■

2. A copper or wooden nail will not become
a magnet when a magnet touches it. Hence
it will not attract the small nails.

3. The process of temporary magnetization is

9

called induction. The induced magnetism is

wmmmmmmmrnm

Explanation

1 . When the magnet touches the long iron nail,
it becomes a magnet. Hence it attracts the
small nails or any other magnetic material.

The tiny molecular magnets in

A

[ align themselves systematically
he magnet touches the nail, but
lar magnets become haphazard

when the magnet is removed.

.

Quest 78

1. Small iron nails 5-10 pieces

2. A bar magnet

w

3 . An exercise book

4. A glass of water

9

1. Place the nails over the exercise book.

2. Place the bar magnet below the exercise

magnet and hold it outside near the bottom
of the glass and rotate it round the glass.

Students to enquire

1. Does the magnet affect the iron nails through

the exercise book ?

2. Docs the magnet affect the iron nails through
the water ?

fl,

3.

book, observe that the magnet affects the
iron nails when the magnet is moved below
the exercise book.

Take 3 / 4 lh glass of water and drop a few
iron nails in the water. Now take the bar

Explanation

llllill

1 . Yes, the iron nails are affected by the magnet
through the exercise book.

2 . Yes, the magnet affects the iron nails through
the water.

Quest 79

Materials

1 . A bar magnet

2. An iron bar resembling a bar magnet

What to

1. You have to identify which one is the
magnet and which
one is an iron bar.

2. Touch the end of
one bar at points
A, B, C of the
other bar.

3. Observe what hap-
pens.

4. Now change the
bars and do the

9

same operation
and observe the
nature of attraction
at the ends and in
the middle.

Students to

enquire

1. Why will one bar
attract the other
bar at all points ?

What does that
prove ?

2. When you reverse

the bars you will
observe there is no attraction in the middle,

why

Explanation

1 . If the bar magnet is touched at points A,

B and C of the other bar, then it will

points

magnet

one is an iron bar.

0

2. If the iron bar is touched at points A, B

and C of the magnet, then there will be
attraction at A and C, but no attraction at
B. The centre of a magnet is a neutral
point.

Quest 80

Materials

1 . A used safety razor blade

P

2. A strong bar magnet

3. A magnetic needle
What to do ?

1 . Place the blade on the table and hold it with
a finger.

2. Hold the bar magnet vertically and press it
on the blade at one end.

Students to enquire

1 . Why does the blade become a magnet ?

2. If you rub the north end of the magnet, what
will be the polarity at A and B ?

3. If the end of a blade after magnetisation
repels die north end of a magnetic needle,
what polarity is formed at that part of the

4. What polarity is formed in the other end ?

3. Then draw the magnet from end A to end
B and then raise the magnet and draw it
again from A to B.

4. Do it four or five times. The blade will
become a magnet.

5. Bring one end of the blade near the north
end of a magnetic needle. Observe what
happpens.

6. Now bring the other end of the blade near
the north end of the magnetic needle. Observe
what happens.

1. When the blade is rubbed with the magnet
each tiny molecular magnet in the blade
gets aligned systematically and becomes a
magnet.

2. The end A becomes the north and the end
B becomes the south.

3. If an end of a blade after magnetization
repels the north end of a magnetic needle,
then that end is the north pole.

4. The other end of the blade is the south pole.

Quest 81

Molecular magnetism

d

Materials iiiiMiii

1. A test tube

2. Iron filings

3. A bar magnet

4. A magnetic needle

What to do

1. Fill the tes

m

fourths

filings. Close the mouth of the test tube
with paper.

2. Spread the iron filings evenly in the test tube

♦

and keep it horizontal.

3. Take one end of the test tube at right angle
to the needle towards the north and the south
end of the needle and observe I

same

pole

4.

north

magnet over one end of the test
tube and take the magnet along
the test tube to the other end.

Repeat the operation three or

four times.

5. Now, take the end of the test

tube, from where the rubbing

was started, towards the north pole of the
magnetic needle. You will observe that the
needle will be repelled.

6. Now, bring the other end of the test tube
towards the north pole. You will observe
that the needle will be attracted. It proves
that the test tube behaves like a bar magnet.

7. Now, shake the test tube and repeat the
operation. You will observe that the needle
would not be deflected .This proves that the
test tube does not behave like a bar magnet.

Students to enquire MHMMi

1 . Before magnetization why did both the ends

of the test tube get attracted by the magnetic

♦

needle ?

2. How was the test tube converted into a
magnet ?

3. How does this experiment explain the mo-
lecular theory of magnetism ?

Explanation

magnetic

The

the ends are attracted by the magnetic needle.
When the test tube is rubbed with a magnet.

magnetised

arrange

behaves like a bar magnet.

3.

All the molecules in a magnetic substance
are small magnets. Normally, the molecular
magnets are arranged in domains in such a
way that the substance does not show any
magnetic property. But when the magnetic
substance is magnetized, the molecular
magnets align themselves in such a way that
the substance shows magnetic property.

Quest 82

Materials

1 . A bar magnet

2. A plastic sheet

3. A thin iron sheet

4. A few small nails
What to do ?

1 . Hold the magnet vertically and place the

plastic sheet below the magnet. Now, bring
the magnet with the plastic sheet near the
nails. You will observe that the nails are
attracted by the magnet and they stick to the

2. Why do the nails fall off when the iron sheet
is introduced ?

3. Will the nails fall off if a copper or alu-
minium sheet were introduced instead of the
iron sheet ?

Explanation

1 . The magnetic lines of force pass through the
plastic sheet. Hence the nails are attracted
owing to magnetic induction.

2. When an iron sheet is introduced the
magnetic lines of force get concentrated in

sheet though there is no direct connection
between the magnet and the nails.

2. Now, raise the magnet a little and intro-
duce the iron sheet over the plastic sheet.
You will observe that the nails fall off the
sheet.

Students to enquire tmmmmmMMm

1 . Why do the nails stick to the plastic sheet
even though the nails do not touch the

magnet

?

the iron sheet and do not pass through the
iron sheet. Hence the magnet cannot induce
magnetism in the nails. So the nails fall off.
This is called magnetic screening.

3. If a copper or aluminium sheet were intro-
duced, then the nails would not fall off.
This is due to the fact that aluminium and
copper are not magnetic substances. Non-
magnetic substances cannot screen the lines
of force.

Quest 83

Rainbow on paper

*, * ■ P • * * > ■ P •» m M M ■ ■ ■ A

9 B*9»mmmT* r P F f W* l

mKmmrmmr m + *upmvm*w*

Materials

1 . Water in a container

2. A minor

3. A white sheet of paper

What to do ?

1 . Place the mirror in the container in such a
way that the major part of the mirror is
below the water.

2. Do the experiment in sunlight. Try to reflect
the sunlight on the paper with the mirror.

surface of water ?

2. When the sunlight falls on the water, what
happens to the light ?

3. How is the rainbow created on the paper ?

Explanation

1. If the sunlight falls directly on the minor,
the light gets reflected.

2. When the light falls on the surface of the
water, it gets refracted.

t

3. Sunlight is composed of seven colours. When

You have to keep the paper fixed and the
reflection of sunlight should take place from
that part of the minor which is below the
water. You have to adjust the mirror, if
necessary.

Students to enquire
1 . What happens if the sunlight falls on that
portion of the mirror which is above the

the sunlight falls on the surface of the water,
the seven colours are refracted at different
angles and are separated. When these colours
fall on the submerged portion of the mirror,
they get reflected. When these different
coloured lights come out of the water, they
form the rainbow on the paper.

Quest 84

Materials

1. A bowl

2. A coin

3. Water
What to do ?

1 . Place a coin at the centre of the bowl.

2. Place your eyes in such a positon that the

4. You will observe that the coin suddenly
comes into your sight though you have not

• %

Students to enquire

1 . Why could you not see the coin when you
placed your eyes as at point A?

2. Why does the coin reappear again?

Explanation
1. We see an object
^ when light from

that object comes to
V our eyes. Because

/pj. the rim of the bowl

^ ? I obstructed the light

J from reaching our

eyes we could not

*

coin just vanishes from your sight. Keep
your eyes fixed there (Fig. A).

3. Now let your friend gently pour water into
the bowl without displacing the coin.

P sec the coin.

2. When light rays
pass from one me-
dium to another,
they bend from their
original path. This
- — - bending of light is

called refraction.
When light passes
from a denser to a
rarer medium it
bends away from

the normal to the

water surface. Due to this an object in water
is seen raised. This refraction of light from
the water surface made the coin visible.

Quest 85

1. A comb.

What to do ? mmmmfMWMmmBm.

1 . Hold the comb with your left hand. Draw
your finger over the teeth of the comb from
one end to the other. Listen to the sound.

2. Now, keep the comb j
vertically on the table.

Repeat the operation.

You will observe that the
intensity of sound has
increased .

3. Keep the comb on other
objects and repeat the

experiment.

Students to enquire

1. Why does the comb make /

a sound when you draw / j

comb ?

2. Why does the sound in-
crease when you keep the
comb on the table and
comb ?

3. Where is this method of
increasing the sound

utilised ? I —

Explanation

1 . When you draw your finger over the comb,
the teeth start vibrating. A vibrating body

out

When

held in the air, only the teeth and the comb
start vibrating. But when the comb is held
on the table a forced vibration is set on the
table also. Owing to the combination of
these two vibrations of the comb and the
table the intensity of sound is increased.

m

u

c.

\

3. In different instruments like the sitar, the
sarod, the violin, the tanpura there is a hollow
box made of wood or other material. This
increases the sound when the instrument is
played.

Quest 86

Materials

1 . A narrow-necked empty bottle

2. Water

3. A scale or a key

What to do ?

1 . Fill the bottle with water keeping a little
gap at the top. Blow air at the mouth and
try to bring out sound like a flute. Notice
the pitch of the sound.

2. Reduce the water of the bottle in steps and
repeat the activity. Notice the pitch of the
sound as the water level goes down.

bottle as the water level goes down ?

2. Why does it change so ?

3. What happens to the pitch of the struck
bottle as the water level goes down ?

4. Why does it change so ?

1 . As the water level goes down the pitch of
the whistle sound also goes down.

2. The length of the vibrating air column in-
creases as the water level goes down. The
pitch of vibrating air column is inversely
proportional to its length. Hence, the more

3. Now, fill the bottle again with water and
strike the bottle with the key or the scale.
Notice the pitch.

4. Reduce the quantity of water in steps and
repeat the activity. Notice the pitch of sound
as the water level goes down.

Students to enquire

1 . What happens to the pitch of the whistling

the length the less is the pitch.

3. If you strike the bottle as the water level
goes down, the pitch of sound goes on in-
creasing.

4. As you reduce the water , the total mass of
the bottle lessens. The pitch of sound in-
creases with the reduction of the mass of
the bottle.

Quest 87

Dancing paper strips

Materials

1. A plastic comb

2. Some small pieces of paper
What to do ? WMMMBmm

1. Take the dry comb and coml

two or three times.

2. Then, brine the comb near

wmmM

are

attracted by the comb.

What

a

a

Explanation

1. When the hair is combed

When

near

Opposite

tract

the pieces of paper, thread or aluminium

a

^ ^ '

sv

see

the pieces of paper are attracted.

Students to enquire

1 . Why are the pieces of paper attracted by the

comb ?

2. If the comb is negatively charged, what is
the charge formed in the pieces of paper or
aluminium foil ?

foil.

If the comb is negatively charged the pieces
of paper or aluminium foil or thread will be

positively charged.

>lastic, glass or ebonite rods
flannel or silk they will be

charged.

Quest 88

Materials

mmm?

1 . A plastic comb

2. An empty powder can with a hole at the
bottom

3. A bucket
What to do ?

1 . Fill the can with water and let the water fall
into the bucket.

wmlf on your hair and hold the
comb near the flowing water.

3. You will observe that the water stream will
be attracted towards the comb.

4 . If the comb or the hair is wet, the experi-

ment will not work.

Students to enquire

1 . Why does the water stream tiend towards
the comb ?

2. Will a thick stream of water bend ? If not,
why ?

3. Why does not the stream bend if the comb

is wet ?

mmmm

4. What else can 1

€

sides a comb ?

Explanation

1. When the hair is combed
the comb becomes chatged.
When the charged comb is
brought near the water
stream, the stream gets an
opposite charge by induc-
tion. This is why the stream
gets attracted by the comb.

2. As the attractive force of
static electricity is very
feeble it cannot bend a thick
stream.

3. If the comb or the hair is
wet, the comb will not be
charged. This is the reason
why in the rainy season the
static electricity experiments

performed

4.

balloon

plastic cards

wool

flannel

Quest 89

Materials
1 1 Sugar and p
2. A dry comb
What to do

mmmmm

2. Why are

powder

3. In what other ways can you separate the

pepper powder from the sugar ?

* . . . .

Explanation

1.

powder

When

2 .

ifiiA r i *

it on a piece of paper.

Comb your hair and bring the comb near the

mixture of sugar and pepper powder. You
will observe that the pepper powder will be
attracted very easily by the comb. Collect
the powder on a piece of paper by striking

the comb on the table.

When you

vnui^vui «r ^ % *

near the mixture, the opposite charge is in-

l thp

powder

granules of pepper are attracted by the comb

The

chemical composition

tUllIU UVVUMtyv

3 if we mix sugar and pepper powder in water.

3. You can seperate all the pepper powder by
repeating the operation several times.

4. You will observe that if you do not comb

« Ml a . U ^

sugar will be dissolved in water, but pepper

^ M V/Ml

powder

powder

granules

0

attracted by the comb.

Students to enquire HiHIK

1 . Why are the pepper granules attracted when

you use the comb after using it on hair ?

separate it from the sugar solution. If you
now evaporate the water of the sugar solu-
tion, sugar crystals will be left. In this way
also you can separate the two compounds
nf thr. suear and pepper powder mixture.

Quest 90

W&mm.

ill

Materials
1. Three balloons
What to do ?

1 . Rub the balloons on your shirt.

2. Take the balloons close to a dry wall. You
will observe that the balloons get stuck to
the wall.

mmmsmm

Students to enquire
1 . Why are the balloons rubbed on the shirt ?

2. Why do the balloons stick to the wall ?

3. Why is a dry wall required for the experi-
ment ?

4. Will the balloons stick for ever to the wall?

wmm

Explanation

1 . The balloons are rubbed on the shirt to get
them charged.

2. When the balloons are rubbed, some elec-
trons pass from the shirt to the balloon.
Normally there are equal numbers of pro-
tons and electrons in an uncharged object.
Hence the object is electrically neutral. But,
when excess of electron accumulates on the

balloon it gets negatively
charged. When negatively
charged balloons are brought
near the wall, the electrons
on the surface of the wall are
repelled. Thereby the wall
gets positively charged. Un-
like charges attract each
other. Hence the balloons get
stuck to the wall.

3. If the wall is wet, it will lose
charge very quickly. The
same thing happens if the air
is very humid. Hence the wall
has to be dry.

4. If the balloons arc kept on
the wall for long, then the
excess electrons from the
balloons will flow back to
the wall. The balloons will

become neutral and will fall. Moreover, if
the balloons are kept for long, they will

Quest 91

t

Materials

that the comb will attract the scale and it

wooden

tumble down

2. A dry comb

Students to enquire

What

Why

the

Explanation

such a way that the 6" mark is in line with

the edge of the table and the scale just

When the charged comb

balances.

opposite

2. Brush your dry hair with the comb and

duced in the scale and the scale is attracted

bring the comb below that end of the scale

by the comb.The scale loses its balance and

MW

which is outside the table. You will observe

down

Quest 92

Material

1 . A piece of asbestos or a metal plate

2. An ink dropper

3. Aluminium dust

4. Iodine crystals
What to do ?

1 . T ake one teaspoonful of iodine crystals and

same

powder

4. After a little while you will observe that
smoke starts coming out and then the re-
agents catch fire.

2. Mix the powders on the plate and give the
mixture the shape of a cone and make a
depression on the top.

3. With the help of a dropper, let one or two
drops of water fall on the top of the heap.

Students to enquire

1. Why do you have to grind the iodine
crystals ?

2. Why do the reagents have to be dry ?

3. Will the reagents react without water ?

4. Where in our daily life does water produce

a reaction like this ?

Explanation

1. If you crush the iodine
crystals, the contact area
between the two reagents
increases. This increases
the rate of reaction.

2. If the reagents are wet,
the heat created by the
reaction will be absorbed
by water and the rate of
reaction will be lowered.
For this reason the re-
agents will not catch fire.

3. Water acts as a catalyst.
Reaction will not start
without water. Water first
helps in starting the reac-
tion in a few molecules.

%

This causes generation of heat which in turn
helps in further reaction.

4. In our daily life, rust is formed because of
similar reaction aided by water.

Quest 93

Materials

ink

500 c.c. round-bottomed

2 . A two-holcd rubber stopper with a long
glass tube in one hole and an ink dropper

in the other hole

3. A test tube with a rubber stopper through
which there is a bent tube

4. When will the water start entering the flask?

5 . Why does the water enter the flask like a

fountain ?

500

(NH

4 '

carbonate

lamp

Explanation

1 . When ammonium chloride and calcium car-
bonate are mixed together and heated, am-
monia gas is formed. The following reaction

takes place :

2NH 4 C1 + CaC0 3 = 2NH 3 + CaCl 2 + H 2 0

2. Density of ammonia ‘ " “

“MNB

What

1. Take NH 4 C1 and CaC0 3 in the test tube.
Close the mouth of the test tube with the

stopper and heat it.

2. Fill the ink dropper with water.

3 . Invert the flask and introduce the bent tube

You will get the pungent smell of ammonia.
Continue heating the flask for a few seconds

Then close the mouth of the flask with

4

the rubber stopper having the long tube and will rise up in the air. Hence the flask has

•i « . 1 J ^ rl a

ink

5

A A

to be held upside down.

3 . Ammonia is very soluble in water. So, when

of the long tube in the beaker of water. . ... m

Sprinkle a little water inside the flask by ga s gets dissolved in water and a partial

vacuum is created inside the flask.

will observe that water will enter the flask 4. The

like a fountain.

Students to enquire

1 . What happens when the two
mixed together and heated ?

2. Why do you have to inver

collect the gas ?

3 What is the function of water 1

a partial vacuum is created inside the flask.
5. After the partial vacuum is created inside
the flask atmospheric pressure working on
the water in the beaker forces the water
inside flask to gush like a fountain. The
narrower the end of the tube the better will

be the fountain effect.

Quest 94

mm *

ii

mmrnmmmmm

m

mm

Cooling by shaking

^^SSSKSS

Materials ^OM M MMM

1 . A conical flask with a rubber stopper

2. Barium hydroxide (Ba(OH) 2 ) and ammo-
nium thiocyanide (NH 4 SCN)

What to do ?

1 . Take one teaspoonful of each chemical in

the two chemicals ?

Why should the wooden board

Explanation

When two compounds react with each other
either heat is given away or taken in. If heat
is given away, it is called exothermic reac-
tion, and if heat is taken in, it is called

Close the mouth with the stopper and shake
the flask for some time. After shaking it for
some time you will observe that the flask is
getting cooler.

If you keep the flask on a wet wooden board,
it will stick to the board.

Students to enquire

1 . What kind of reaction takes place between

endothermic reaction. The above reaction is
endothermic. Hence, it takes heat away from
its environment i.e., from the flask. Hence

2. When the flask gets cooler, it cools the
water of the board to ice. Because of this,
the flask gets stuck to the board.

Quest 95

mm

*tppp

m m m ^

*

Which gases are formed

sm

sek

ipp* 8 *

Explanation :

1 . Zinc granules, calcium carbonate (CaC0 3 )

2. Potassium chlorate (KC10 3 ), dilute hydro-
chloric acid (HC1)

4 • • • • I.

% _ •

3. A spirit lamp or a heater

4. Three test tubes, a match box and a little
ash.

what to do ? mmmmm wmmmmmm

9 •

• 9 * «

1 . Take Zinc granules in the first test tube and

add 3-4c.c. HC1 to that. Close the mouth I

* ■

of the test tube with your thumb. After
sometime take away your thumb and
bring a lighted matchstick near the mouth
of the test tube. You will observe that
there will be a small explosion.

2. Take CaC0 3 (pieces of marble) in the
second test tube and add 3-4 c.c. of HC1.
Introduce a burning stick into the test
tube. You will observe that the fire will
extinguish.

3. Take a little KC10 3 mixed with ash in
the third lest tube. Heat the test tube.
Light a wooden stick and put it off and

then immediately introduce the stick into |

the test tube. You will observe that the stick

will again light up.

Students to enquire

.SV.'.V.V.

Which gas was formed in the first test tube
and what is its characteristics ?

9

Which gas was formed in the second test
tube and what is its characteristics ?
Which gas was formed in the third test tube
and how is it different from the other two ?

Zn

formed

ZnCl-.

highly inflammable. So, when the lighted

• «

matchstick is brought near it a small ex-

• * ft

ft .< • ■

• •

plosion takes place.

formed

This

combustion. It is denser than air and is

colourless. CaC0 3 + 2HC1 = CaCl 2 +C0 2
+H 2 0.

3. Oxygen is formed in the third test tube.
Oxygen helps in combustion but is not itself
inflammable like hydrogen. Hence, when a
lighted stick that has just been extinguished
is brought in contact with oxygen the stick
is ignited again. Oxygen makes up about
20% of atmospheric air.

Quest 96

Materials

1 . Sodium peroxide (N^Oj)

2. Lycopodium powder

3. An ice cube

w

4. A metal sheet
What to do ?

1 . Take two teaspoonful of lycopodium pow-
der in a heap on the metal plate, give the

heap the shape of a cone.

%

2. Put half a teaspoonful of sodium peroxide

« . r .

5. Is the reaction that takes place exothermic

* * * • # * . v •
*••• • , « » *

or endothermic ?

• * * • • _ •

6 . What else can you use in lieu of lycopodium

*

powder ?

Explanation

1 . When ice is kept at room temperature, it will

• •

melt into water.

• " %

• *

2. NajOj + H 2 0 -> NaOH + O n + energy
(heat).

3. Sodium peroxide supplies oxygen for spon-

on the top of the heap. Put the piece of ice
on it.

3. Stand a little distance off. You will observe
that the lycopodium powder will be ignited.

Students to enquire

1 . What happens to the ice when it is kept at
room temperature ?

2. What reaction occurs between sodium per-
oxide and water ?

3. What is the function of sodium peroxide ?

4. Why is the lycopodium powder ignited ?

tancous combustion.

4 . Reaction takes place between sodium per-
oxide and water from melted ice nascenf
oxygen is formed, nascent oxygen is very
reactive. It oxidizes the carbon in the lyco-
podium powder and spontaneous combus-
tion starts. This sets the lycopodium powder
into flame.

*

5. The reaction is exothermic.

6. You can use tissue paper, fine saw dust, or

Quest 97

■■■■ft

Materials

1 . Calcium hydroxide (Ca(OH) 2 )

2. A test tube

3. A drinking straw

4. Filter paper

What to do ?

1 . Fill half the test tube with calcium hydrox-
ide solution. If Ca(OH) 2 is available in
powder form, then pre-
pare a saturated solu-
tion of Ca(OH) 2 in
warm water, keep the
solution for some time

*

and then filter out the
clear water from the
top.

2. Blow air into the solu-
tion through the straw.

You will observe that
the solution starts be-
coming cloudy due to
the formation of a
white precipitate.

3 . If you continue blow-
ing air into the cloudy
clear up.

Students to enquire

1. Why does the precipitation take place ?

2. Normally, when does precipitation occur ?

3. Why docs the precipitate disappear ?

dioxide (C0 2 ) is added to the solution. CO z
reacts with calcium hydroxide (Ca(OH) 2 )
and calcium carbonate is formed which is
insoluble in water. Hence a precipitate is
formed. C0 2 + Ca(OH) 2 = CaC0 3 + H 2 0.

2. When the solubility of a substance in a
liquid is less, precipitation takes place.

3 . When you continue blowing more C0 2 into

1. When you blow into the solution carbon

the precipitate calcium bicarbonate
(Ca(HC0 3 ) 2 ) is formed. CaC0 3 + H 2 0 +
C0 2 = Ca(HC0 3 ) 2 , Calcium bicarbonate is
soluble in water. Hence the precipitate dis-
appears.

Quest 98

Materials

1. A 250 c.c. conical flask with rubber

stopper

2. 5 gms. potassium or sodium hydroxide

3. 3 gm. glucose or dextrose

4. Methylene blue

What to do ?

1 . Dissolve 5 gms. potassium hydroxide and 3

2. Why does the colour disappear on keeping
still ?

3. Can the experiment be conducted
repeatedly ?

4. What is the nature of the chemical reaction

which is taking place ?

1 . In an alkaline solution of a reducing sugar,

gms. glucose in water in the flask. Add a | methylene blue is reduced to a colourless

few drops of methylene blue in the liquid.
A colourless liquid will be formed.

2. Close the mouth of the the flask by the
stopper and shake the flask. You will ob-
serve that the colourless liquid be changed
to a deep blue colour.

3. Keep the flask on the table for some time.
The liquid will again become colourless.

4. Shake the flask and the deep blue colour
will appear again. Keep the flask still for
some time and the colour will disappear.

Students to enquire

■HHB

1 . Why does the deep blue colour appear on

shaking ?

compound. On shaking, the oxygen in the
air inside the flask dissolves in the liquid
and the colourless solution is rcoxidized into
the blue dye. The solution turns deep blue.

2. When the flask is left still for some time,
the oxygen goes out of the solution. The
solution is reduced again and its colour

3. The experiment can be repeated several
times but after a few days the solution will
turn yellow and then brown.

4. It is a reversible oxidation-reduction
reaction.

Quest 99

* • * 4 •

Materials

1 . Six test tubes on a stand

. ♦ *

2. Dilute hydrochloric acid

3. Liquid sodium hydroxide

4. Phcnolphthalcin

5. A drinking straw

fi A glass and an ink drODi

•I

What to do ?

1 . Number the test tube 1 to 6 from the left.

2. Place three drops of phenolphthalein indi-
cator in the test tubes 2 and 4. Take one
drop of sodium hydroxide in the test tube

3.

4

6 and in the glass. Take three drops of
hydrochloric acid in the test tube 5.

Fill the glass three-fourths full with water.
Now fill the test tubes 1 , 2, 3 and 4 half full
with water from the glass. You will observe
that the liquids in the test tubes 2 and 4 turn
pink.

Now, pour the liquids from the four test
tubes into the glass.

5. Now fill the test tubes from 1-5 with the
liquid from the glass. Except in the test-tube
5, liquids in all other test tubes will show
pink colour.

6. Now pour the liquids from all the test tubes
into the glass and fill up again all the six
test tubes. You will observe that only the

Students to enquire

pinkish

Why

pink

Why does the liquid

colourless ?

Why does the liquid
pink colour ?

\

Explanation
1 . Phenolphthalein is an indicator for alkaline

pink

There

phthalein in test tubes 2 and 4 and sodium

When water is

in the glass an alkaline solution is created.
So, when the alkaline solution is added to
the test tubes 2 and 4 the phenolphthalein

2. There is hydrochloric acid in test tube 5.
When the pink alkaline solution is poured
into the test tubes 1 to 5, the alkaline so-
lution is neutralised by the hydrochloric acid
in the test tube 5. Hence the liquid in the test
tube 5 becomes colourless. Phenolphthalein
is colourless in neutral solution.

3. As the test tube 6 contains sodium hydrox-
ide, the solution becomes alkaline again and
phenolphthalein in alkaline solution turns
pink in colour.

Quest 100

• *

Materials

S a 9 f

9 a

1 . A stick one metre long,

2. Filter paper

• 9 # § » •

3. Iodine crystals

4. Concentrated ammonia

5. A 100 c.c. beaker
What to do ?

1. Dissolve iodine crystals in concentrated

ammonia in the beaker. Be sure that all the
crystals are dissolved. Stir the liquid with
a glass rod. '

2. Let the beaker stand in the air till a brown
residue is left in the beaker.

3. When the residue is still wet, scratch out the
residue with the help of the stirrer on the
filter paper. Allow it to dry. It will take

» • .. # " m 4

about an hour to dry. The more dry the
residue the better the experiment.

4. Stand about a metre apart from the filter
paper and then tap the dried up crystals with
the help of the long stick. Tap only a few
crystals at a time because the crystals are
highly explosive.

* k

Students to enquire

1. Which compound is formed when iodine
crystals are dissolved in concentrated
ammonia ?

2. Why is the compound so explosive ?

3. Why do we hear a loud report when there
is an explosion ?

4. Is oxygen always needed whenever there is
an explosion ?

Explanation

1 . When iodine crystals are dissolved in con-
centrated ammonia, nitrogen tri-iodide is
formed.

2. Wet nitrogen tri-iodide is not that danger-
ous. But when much of ammonia gets evapo-
rated, dry nitrogen tri-iodide becomes un-
stable. When it is tapped by the stick, it
explodes. If the amount of nitrogen
tri-iodide is less, then there is less danger of
a big explosion.

3 . As a large amount of gas is produced during
an explosion, there is a loud sound.

4. When there is a sudden release of a large
volume of gas, there is a loud sound. As for
example, when a balloon is pricked the air
under pressure is suddenly released. Hence,
there is a loud sound. Oxygen is not
indispensible for an explosion to occur.

Quest 101

-mmi W&

w?

Acid heats up

fP^'

p

Materials

#p-£

1. Potassium chlorate (KQO 3 )

2. Potassium permanganate ( KMn0 4 )

3. Ground sugar

4. Concentrated sulphuric acid (H 2 S0 4 )

5. An ink dropper, a watch glass

What

WMi

1 .

potassium

potassium permanganate

2. Pour a drop of sulphuric acid

on the heap of the mixture with

the help of the dropper. Drop

the acid from a distance. It is

ment in the open. Take great

care while handling the acid.

You will observe that the mix-

ture will catch fire and a large

volume of gas will be produced

If a little barium, strontium.

copper or sodium salt is added

to the mixture, then you will

observe the magic of colours.

Students to enquire

1 . What is the source of energy

for the generation of heat ?

2. Which one among the

kinds of powder was burning 7

3. Where did the heat come from

for the spontaneous combustion ?

Which gases are formed

1 . The chemical energy stored in the chemical

compound

2.

powder that was burning

3. Sulphuric acid supplied the first heat to

potassium

The heat helped

potassium chlorate. This

gen oxidized the sugar and so much heat

was liberated that the sugar caught fire.

Potassium chlorate (KC10 3 ) supplied oxy-

_ . -

4

gen for combustion.

5 . Carbon dioxide and water vapour are formed

by combustion.

Quest 102

Invisible writing

mm

mm*®**

1 . Cobalt chloride crystals

2. Ammonium chloride

3. Distilled water

4. A little cotton

5. A piece of pink paper

%

6. A candle, a match box and a wooden stick

What to do ? gHB I B855S

1. Mix 1 V 2 gms. ammonium chloride with
2V 2 gms. of cobalt chloride. Add 50 c.c. of
distilled water and make a solution. You
will observe that the colour of the solution

will be deep pink.

5. You will observe that the word “chemistry”
will reappear in bright blue colour. When
the paper cools down the inscription disap-
pears again.

Students to enquire WMMMmmim

1 . When you write on the pink paper, why does
it disappear when the paper dries up ?

2. Why does the inscription reappear on
healing ?

3. Why does the inscription disappear again
on cooling ?

Explanation VmHmmmmmmmmmm

1. As the colour of both the paper and the

Wrap a little cotton at one end of the stick.
Dip the cotton in the solution and write the
word “chemistry” on the pink paper.
Allow the paper to dry, you will observe
that the inscription will gradually disap-
pear.

Now, light the candle and bring it near the
paper so that the written word may get the
heat from the flame of the candle.

solution is pink, inscription disappears.

2. When cobalt chloride goes into solution, a
complex compound is formed which releases
water on heating. In this condition the colour
of the compound is blue.

3. When the paper cools, it absorbs moisture
from the atmosphere and the pink colour of
the solution reappears. Hence inscription
disappears again.

Quest 103

Materials

1. 100 grams sugar

3. A small glass tumbler

4. Concentrated sulphuric acid

What to do ?

%

1 . Fill half the glass and the jar with sugar.

2. Pour some water in the glass and about
40 c.c. of concentrated sulphuric acid in the
jar.

3. Wait for some time. You will
observe that in the glass the
sugar will dissolve in water. But
in the jar a blank voluminous
substance will be produced
which will gradually rise up in
the jar and come out of it.

Students to enquire PM*

1 . What is the black substance in
the jar ?

2. What is the difference between
the processes that take place in
the glass and in the jar ?

3. What difference did you
observe in the experiment be-
tween the physical and chemi-
cal processes ?

4. From which container can you

separate the sugar and how ?

5. What happens in the jar ?

Explanation

1 . The black substance in the jar is charcoal.

2. The process that takes place in the glass is

mm am

m&m

a physical change. But a chemical change
takes place in the jar.,

w

3. In a physical change you can bring back the
original substances. But in a chemical change
original substances cannot be brought back
easily.

4. You cap separate the sugar from the sugar
solution in the glass by the evaporation of
water by heating.

5 . The sulphuric acid reacts with sugar chemi-
cally. As a result, charcoal, sulphur dioxide
gas and water vapour are formed. These
gases cause the expansion of charcoal into
a voluminous mass.

Quest 104